Ultra high frequency radio direction finding



March 11, 1941. s, BOND 2,234,331

ULTRA HIGH FREQUENCY RADIO DIRECTION FINDING Filed July 27. 1938 2 sheets-sheet 1 OUTPUT F'HOM B 90 BEHIND /7 /A/ P/l/JJL' WHEN COMB/NED ISnventor Donald {51 Bond D. s. BOND ULTRA HIGH FREQUENGI RADIO DIRECTION FINDING Filed July 27, 1938 2 Sh8etS$h9et -;3 Q

Ihwentor onald 25'. Band Gttorneg Patented Mar. 11, 1941 UNITED, STATES ULTRA HIGH FREQUENCY RADIO DIRECTION FINDING Donald S. Bond, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application July 27, 1938, Serial No. 221,488 7 Claims. (01. 250-11) This invention relates to ultra high frequency direction finding receivers. More specifically, the invention relates to an ultra high frequency receiver which indicates departures to the left or right of a desired course or in which the directive antenna array may be manually or automatically oriented to indicate the bearing of a source of radio frequency radiation.

Numerous arrangements for determining the bearing of a source of radio frequency energy have been described. In one system currents induced in a non-directive antenna are combined with the currents produced in the directive antenna whereby the di ective characteristic of the two antennas becomes that of a cardioid. If the currents from the-directive antenna are periodically-reversed and if the output indicator of the system is reversed in synchronism with the aforementioned reversal, the indicator will show departures to the left or right of the bearing of the source of radio frequency energy. In systems of this type it is customary to use a loop antenna as the directive antenna and a vertical .antenna as the non-directive antenna. While such systems are satisfactory for frequencies as high as 30 megacycles, they are not entirely satisfactory at higher frequencies and at ultra high frequencies of the order of 100 megacycles and upward the loop may prove unsatisfactory as a direction finder when used at its null point.

As one of the primary objects of this invention, means are provided for indicating the bearing of the source of ultra high frequency radiation. Another object of this invention is to provide means for overcoming the disadvantages experienced when the conventional direction finder equipment is used within the ultra high frequency range, A further object is to provide means for combining the currents from a dipole antenna array whereby departures to the left or right of a desired course toward a source of ultra high frequency radiation may be determined. A still further object is to provide means whereby an ultra high frequency antenna array may be automatically oriented to indicate the source of ultra high frequency radiation.

In describing the invention reference will be made to the accompanying drawings in which Figure 1 is a schematic diagram of one embodiment of the directive antenna array;

Figure 2 is a graphic illustration of the characteristic field pattern derived from the directive antenna; and

Figure 3 is a wiring diagram illustrating one embodiment of the invention.

In describing this invention'where reference zcntal dipole B is arranged at a distance of wave length from A and is connected by a transmission line 3, which has length of 1 plus A; wave length, to the terminating impedance 'Z0. If each of the dipoles have an effective length equal to of the received wave length and if the difference in the length of the transmission lines is equal to A of the received wave length the directive pattern of the array in the plane of the array will be approximately a circle tangent to the array and a pair of small lobes. Such a div rective pattern is indicated by the solid line 5 of Fig. 2. If means are then-provided for making the phase difference of the currents from A and B become alternately plus 90 degrees and minus 90 electrical degrees, the directive pattern of the array will be alternately the solid line 5 and the dash line 7 of Fig. 2. The application of such an array will be considered in connection with the schematic'circuit diagram of Fig. 3. Referring to Fig. 3,'a horizontaldipole A having an effective length of wave is connected through a transmission line I to a resonant circuit 9 which is coupled to a second resonant circuit ll. -One terminal of the second resonant circuit is grounded. The other terminal is connected through capacitors l3, I5'to'th'e input circuits of a pair of tubes I1, I 9, The input circuits of the tubes "I1, l9 are also connected through series resistors 2I';'23 to a winding of a transformer 25. The winding 'is grounded at a point intermediate its ends: The primary 2! of this transformer 25 is connected to a source of alternating current 29. The tertiary winding 3| of the transformer 25 will be hereinafter described. v

The output circuits of the tubes l1, 19 are connected in push-pull to a resonant circuit 33 which is coupled to a resonant circuit 35. The last-mentioned resonant circuit 35 is connected to the input circuit of a typical high frequency receiver 3'I.- This receiver may be of the superheterodyne-type including radiofrequency, intermediate and audio amplifiers. aswell as the demodulator and localoscillatol. While, the superheterodyne receiver has been mentioned, the invention is not limited thereto but may be applied to any suitable amplifying or demodulating arrangement. The second dipole antenna B is horizontally arranged and is spaced A wave length from the first mentioned dipole A. The second dipole B, like the first, preferably has an effective length equal to of the received wave. The transmission line 3 which couples the dipole B to the resonant circuit 39 has an effective length which will produce a 90 phase shift with respect to the transmission line I. For example, either line may be A; wave different (or n plus ./4 where n is an integer) from the length of the other line. The terminating circuit 39 for the second dipole is coupled to the resonant circuit 35 which is connected to the input circuit of the receiver 31.

The outer terminals of the tertiary winding 3| are connected respectively to the anodes 4|, 43

of a pair of rectifiers. The cathodes of these rectifiers are connected together by a pair of resistors 45, 41. The junction of the cathode resistors is connected to one terminal of the secondary of the transformer 49. The other secondary terminal is connected to a point intermediate the ends of the tertiary winding. The primary of the transformer 49 is connected to the output of the radio receiver 31,

The principle of operation of the foregoing circuit is essentially as follows: Currents induced in the first dipole A are applied to the input circuits of the amplifiers I1, l9 in parallel but since the input circuits of the amplifiers are also connected in push-pull through the transformer 25 to the source of alternating current 29 it will be seen that the tubes ll, l9 are alternately energized whereby the currents from the first dipole are alternately reversed as they are applied to the input of the receiver.

Currents induced in the second dipole B because of the diiference in the length of the transmission lines I, 3, arrive at the input of the receiver in proper phase to combine with the current from the push-pull circuit H, I9, 33. Thus the radio frequency currents applied to the radio receiver 31 are modulated by the currents from the alternator 29 and have a phase in the output circuit of the receiver which is dependent upon the phase'of the radio frequency currents. If the antennas A and B are so oriented with respect to the waves whose source is tobe determined that no currents are induced in A and B, the rectifiers 4|, 43 will have applied only those currents from the alternator 29 and hence the currents applied to the indicator 5| which is connected across the cathode resistors 45, 41 will be equal and opposite indicating that the receiver is on the desired radial line or course toward the source of radio frequency energy. If, however, the angle between the dipoles and the wave front is such that currents are induced in the dipoles then the demodulated currents in the output of the receiver will be applied through the transformer 49 so that the rectifiers will no longer receive equal and opposite currents but will be unbalanced by the demodulated currents of either or 180 phase with respect to the current in the tertiary winding 3|, whereby the meter will indicate the departure to the left or right of the course, as the case may be.

While the invention has been specifically described by reference to the output indicator which includes rectifiers and a direct current type of meter 5|, it should be understood that the reference phase from the alternator 29 may be applied to one of the coils of a dynamometer and the other phase from the output of the receiver applied to the second coil of a dynamometer meter, or in the event that automatic or self-orientation of the antenna array is desired, the two phases of alternating current may be applied to a two-phase motor which is connected to the array, as described in the copending application of Wendell L. Carlson and Donald S.

' Bond, application Serial No. 196,817, filed March 19, 1938. It should also be understood that more than two elements may be used in the directive antenna array if a different directive pattern is desired. In a similar manner antennas other than horizontal dipoles may be used. For example, vertical antennas may be employed and in that event the directive patterns will be different from that disclosed in Fig. 2. Such difference in the directive patterns will not destroy the utility of the device as the operation does not necessarily depend upon any particular pattern. It is suflicient that the patterns be directive, that such directivity be alternately reversed 180, and preferably that the alternate patterns be similar in shape.

I claim as my invention:

1. A radio direction finder for ultra short wave lengths including in combination a pair of dipole antennas arranged opposite and parallel to each other and spaced apart a substantial fraction of said ultra-short wave length, means for alternately reversing the phase of the currents from one of said antennas, means for combining said last mentioned currents with the currents from the otherof said antennas, means for demodulating said combined currents, and means for indicating the phase of said demodulated currents as a function of the phase of said reversing means to thus indicate the angle between the fronts of said radio waves and said antennas.

2. A radio direction indicating receiver for ultra short wave lengths including a pair of dipole antennas arranged opposite and parallel to each other and spaced apart a substantial fraction of said ultra short wave length, means for alternately reversing the phase of the currents transmitted from one of said antennas, means for shifting the phase of the currents transmitted from the other of said antennas, means for combining said first and second mentioned currents, means for demodulating said combined currents, and means for indicating the phase of said demodulated currents as a function of the phase of said reversing means to thus indicate the source of received waves.

3. A radio direction finder for ultra short wave lengths including in combination a pair of dipole antennas located in the same plane and spaced a substantial fraction of said ultra short wave length and arranged opposite and parallel to each other, a local source of alternating current, means for modulating currents derived from one of said dipoles by currents from said local source, means for changing the phase of currents derived from the other of said dipoles by approximately 90, means for combining said derived currents, means for demodulating said combined derived currents, and means for comparing the phase of said demodulated currents with the phase of the currents from said local source.

4. In a device of the character of claim 3, means for mounting said dipoles in the same plane and spaced substantially one-quarter of the received wave length.

5. A device of the character of claim 3 in which the dipoles are eifectively a half wave length long and spaced one-quarter Wave length.

6. A radio direction finder for ultra short wave lengths including a pair of coplanar dipoles spaced a substantial fraction of said ultra short wave length and arranged opposite and parallel to each other, a first radio frequency circuit, a second radio frequency circuit, a transmission line of fixed length coupling one of said dipoles and said second circuit, a second transmission line having a length differing by substantially one-quarter wave from said fixed length coupling said first circuit and the other of said dipoles, a source of alternating current, a pair of modulators, means for applying said alternating current to said modulators in push-pull relation, means for applying currents from said second circuit to said modulators in parallel relation, means for applying the output currents of said modulators and the currents from said first circuit on a common radio frequency circuit, means for demodulating the currents in said common circuit, and means for indicating the attitude of said dipoles with respect to a wave front including means responsive to said alternating current and said demodulated current.

7. A radio direction finder for ultra short wave lengths including a pair of dipoles, said dipoles being horizontal and arranged in parallel lines spaced substantially a quarter wave length, a first radio frequency circuit, a second radio frequency circuit, a transmission line of fixed length coupling one of said dipoles and said second circuit, a second transmission line having a length differing by substantially one-quarter wave from said fixed length coupling said first circuit and the other of said dipoles, a source of alternating current, a pair of modulators, means for applying said alternating current to said modulators in push-pull relation, means for applying currents from said second circuit to said modulators in parallel relation, means for applying the output currents of said modulators and the currents from said first circuit on a common radio frequency circuit, means for demodulating the currents in said common circuit, and means for indicating the attitude of said dipoles with respect to a wave front including means responsive to said alternating current and said demodulated current.

DONALD S. BOND. 

